Transformer



May IZ, 1925. 1,537,927

L. F. BLUME TRANSFORMER Filed June 16, 1923 2 Sheets-Sheet 1 /Z In ven Car."

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, fl/lsflttorne May 12, 1925. "537,927

L. F. BLUME TRANSFORMER File June 16, 1925 2 Sheets-Sheet 2 'Ficgji.

Inventor:

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by// W M H/s A it OP 6% lit Patented May 12, 1925.

UNITED STATES PATENT OFFICE.

LOUIS F. BLUME, OF PITTSFIELD, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

TRANSFORMER.

Application filed June 16, 1823. Serial No. 645,728.

To all whom it may corwe'm':

Be it known that I, LOUIS" F. BLUME, a citizen of the United States, residing'at Pittsfield, in the county of Berkshire, State of Massachusetts, have invented certain new and useful Improvements in Transformers, of which the following is a specification.

My invention relates to transformers and more particularly to transformers having windings provided with ta s connected to suitable switching means or varying the ratio of voltage transformation between the primary and secondary windings of the transformers.

Thewindings of a transformer are often provided with tap connections leading to a suitable switching means or its equivalent for varying the ratio of transformation. One of the objects of the present invention is to provide an improved arrangement whereby the tap connections of atransformer winding may be varied and the ratio of transformation of the transformer conveniently adjusted without interrupting the current in the load circuit. Even if the change be made quickly, it is usually desirable that it be made without interrupting the supply of current to the load circuit as such current interruption would result in the opening of circuit breakers, the stopping of motors and the temporary failure of current supply to lighting circuits. Another object of the invention is to provide an improved arrangement of tapped transformer windings with suitable means for so adjusting the interconnections between tap leads as to vary the ratio of transformation through a wide range without subjecting the insulation of any part of the winding to voltage stresses greater than the voltage of the external circuit to which the winding is connected.

Other objects and advantages will appear from the following desctription taken in connection with the accompanying drawings in which Fig. 1 shows one embodiment of the invention including the windings of a transformer, one of the windings having tap leads connected to suitable switching means which are for changing theratio. of transformation, Figs. 2, 3 and 4 are simple schematic diagrams of the tapped winding with the switches in different positions to illustrate the manner in which the ratio of transfor mation between the transformer windings may be varied, and Fig. 5 shows a modified form of winding similar to that shown in Figs. 2, 3 and 4 but permitting a greater range of voltage adjustment.

Like reference characters refer to similar parts in the different figures of the drawings.

In the particular embodiment of the invention disclosed in the drawings, current from a high voltage supply circuit is transformed to current of low voltage such as may be desirable for operating an induction furnace. The low voltage winding is divided into four sections 1, 2, 3 and 4 connected in parallel to the load circuit 5 which may lead to an induction furnace or other consuming device. These sections of the low voltage secondary winding are distributed between sections of the high voltage primary winding to avoid objectionably high reactance. The high voltage primary winding shown in Figs. 1 to 4 inclusive is divided into two line sections 6 and 7 and two intermediate sections 8 and 9, these four primary winding sections being sym metrically dis osed to avoid high reactance. A symmetrica arrangement is shown in Fig. 1 where the section 7 is the central section and comprises two parallel connected groups of turns extending symmetrically in opposite directions from one of the line terminals. The section 6 comprises two parallel connected end groups of turns extending symmetrically from the other line terminal. The two intermediate sections 8 and 9 are symmetrically disposed at opposite sides of the central section 7 and between it and the two end groups of turns of the section 6.

The four sections 6, 7, 8 and 9 of the'high voltage primary winding are shown diagrammatically in Figs. 2, 3 and 4 with the associatedmeans for interconnecting these sections in accordance with the invention to vary the ratio of transformation between this winding and the low voltage secondary winding, the latter winding being omitted for the purpose of clearness. These four sections of the primary winding preferably have approximately the same effective number of turns and each is provided with taps distributed at intervalspreferably throughout its length. Of course, if any section of the winding, such as section 6 or 7 as shown in Fig. 1, is formed in two parallel connected groups of turns, then the effective number of turns is determined by the number of turns in each such parallel group.

The two line sections 6 and 7 have their outer ends connected to the two sides 10 and 11 of a suitable high voltage supply circuit. The tap leads from the sections 6, 7, 8 and 9 are connected respectively to the terminals of four multiple terminal switches 12, 13, 14 and 15. The switch levers of the switches 12 and 13 are connected re spectively to the adjacent ends of the intermediate winding sections 9 and 8. The switch lever of the switch 14 is connected through a circuit breaker 16 and a reactance 17 to the inner end of the line section 6 of the primary winding and the switch lever of the switch 15 is similarly connected through a circuit breaker 18 and a reactance 19 to the inner end of the other line section 7 of the primary winding.

\Vith the switch levers all in the extreme sections 8 and 9 are connected in parallel and the sections 6 and 7 are connected in series with each other and with the parallel connected sections 8 and 9. Assuming the preferable arrangement in which all four sections have the same number of turns, then the effective number of turns of the complete primary winding is three times the number of turns in any one section. This is the maximum effective number of turns and therefore the ratio of transformation between the primary' and secondary windings is a minimum and the voltage at the terminals of the secondary winding is a minimum. Obviously, the primary current will divide equally between the primary sections 8 and 9. lYith the switch levers all in the other extreme positions indicated in Fig. 3, the primar sections 8 and 9 are out of circuit and ine ective and the sections 6 and T are in parallel with each other across the two sides 10 and 11 of the supply circuit. The effective number of turns of the complete primary winding under these conditions is obviously equal to the number of turns of any one section and is therefore only one-third as great as under the circuit conditions indicated in Fig. 2. This is the minimum number of effective turns and therefore the ratio of transformation between the primary and secondary windings is a maximum and the voltage at the terminals of the secondary winding is a maximum and three times as great as under the circuit conditions indicated in Fig. 2. Intermediate secondary voltages approximating any desired values between these maximum and minimum values may be obtained by adjusting the switch levers to intermediate positions such as indicated in Figs. 1 and 4.

The method of changing or adjusting .the tap connections is preferably such that electrical balance is maintained at all times as nearly as possible between the different winding sections and their component parts. To this end, the levers of the switches 14 and 15 should make connection with the same relative tap connections of their respective winding sections 8 and 9 to keep the effective number of turns in these two winding sections equal at all times with the exception of a short interval of time during the tap changing operation as will be explained later. It is obvious that if the effective number of turns in one of these winding sections is greater than in the other, a local circulating current in these two sections will result and cause undesirable heating and loss in efficiency. It is also desirable that the levers of the switches 12 and 13 similarly make connection with corresponding tap connections at all times except for an occasional short interval of time during the tap changing operation. By reference to Figs. 2 and 3, it will be seen that those portions of the two winding sections 6 and 7 which are inside the taps to which their respective switch levers are connected are in parallel and that any inequality in the number of turns inside these connected taps will also tend to produce a local circulating current through these turns and the effective turns of the winding sections 8 and 9 and thus produce undesirable heating and loss in efficiency.

The arrangement which has been described and the method of operation is such that the ratio of transformation of the transformer may be adjusted throughout its range without interrupting the flow of current in the load circuit. Assuming that the switch levers are in the extreme positions indicated in Fig. 2 so that the secondary voltage is circuit breaker 16 may now be opened so that HIS no current can flowthrough the intermediate winding'section 8, the switch 14 and the reactance 17. This will not interrupt the'operation of the transformer as the entire primary current will now flow through the other intermediate winding section 9 and the .two line sections 6 and 7 and maintain the secondary voltage substantially unchanged. As the switch 14 is now carrying no current,

its lever may be moved without arcing to its next contact to reduce the effective. number of turns in the winding section 8 and. the circuit breaker 16 may then be closed again when the primary current will again divide between the winding sections 8 and 9 except for those few turns of the section 8 9. The number of effective turns in the winding section 9 is now reduced in a similar manner by opening the circuit breaker 18, moving the lever of the switch 15 to make connection with the next tap of the winding section while the other winding section 8 carries the full primary current, and then again closing the circuit breaker 18 to permit the primary current'to again divide be tween the two winding sections. The effective number of turns has now been reduced in the intermediate winding sections and therefore in the primary winding as a whole and the secondary'voltage is correspondingly increased. The number of effective turns in the two winding sections 8 and 9 is also again equalized so that the primary current will divide equally between them. t may be noted that while the reactances 17 and 19 act in series to'limit any circulating current in the winding sections 8 and 9', the primary current flows through these reactances in parallel. The reactance in the primary current circuit is therefore only one-quarter as great as in the circulating current circuit.

Further increase in the secondary voltage may be produced by changing the positions of the levers of the switches 12 and 13. Opening the circuit breaker 18 will interrupt the current through the windmg section 9 and the switch 12, the entire primary current now flowing through the winding section 8, and the lever of the switch 12 may then be moved to the next contact without arcing and the circuit breaker 18 again closed. The primary current will now divide again into two parallel paths, one path comprising the effective turns of the wind ing section 9 and the other comprising an equal number of effective turns of the winding section 8 together with the few turns be tween the inner two taps of the line section 6. These few turns of the section 6 are unbalanced and will cause a local circulating current in the intermediate windin sections 8 and 9, which current is, however, limited in value as before by the reactances 17 and 19. In a similar manner, the circuit breaker 16 may now be opened, the lever of the switch 13 moved to the next contact while the winding section 9 is carrying the full primary current, and the circuit breaker 16 again closed. The primary current will now divide equally again between the two parallel paths through the intermediate winding sections 8 and 9 because the few turns between the inner two taps of the winding section 7 are in series with the winding section 9 and balance the few turns between the inner two taps of the winding section 6 which are in series with the winding section 8 It will be seen that the changes which have been described in the positions of the levers of the switches 12 and 13 have resulted in changing the turns between the inner two taps of the two line sections 6 and 7 from-series connection in which each of these turns carries full primary current to parallel connection in which'each carries only one half the full primary current. The effective number of turns of the primary winding has therefore been decreased by the number of turns between the inner two taps of either of the line sections 6 or 7 and the secondary voltage has been, of course, correspondingly increased. Fig. 1 shows the circuit arrangement after the levers of the switches 12, 13, 14 and 15 have each been moved one step as has just been described. Fig. 4.- shows the circuit arrangement after each switch lever has been moved one more step. It is obvious that this sequence of steps may be repeated until the switch levers have reached the extreme positions shown in Fig. 3 when the two intermediate winding sections 6 and 7 will be connected in parallel across the primary supply circuit and the two intermediate winding sections 8 and 9 will each be entirely out of circuit and ineffective, the effective number of turns now being equal to the number of turns in one winding section. Assuming as before that all four of the winding sections have the same number of turns, then it has been shown that the secondary voltage may be adjusted throughout a wide range of values, the maximum being three times the minimum with the particular arrangement which has been described.

The range of voltage adjustment maybe increased if desired by increasing the number of intermediate winding sections of the tapped winding as indicated in the modifica- -the switch, 13 and another intermediate winding section 9 provided with tap conne'tions and a switch 15 is connected between the intermediate section 9 and the lever of the switch 12. Each of these additional winding sections 8' and 9 preferably has the same number of turns as each ii? of the other winding sections 6, 7, 8 and 9.

The method of operation is preferably similar to that already described so that the number of effective turns in the two sections 8 and 8 may be always as nearly equal as possible to the number of effective turns in the two sections 9 and 9. Obviously the circuit breaker 16 may serve to interrupt the current through each of the switches 13, 14 and 14 and similarly the circuit breaker 18 may serve to interrupt the current through each of the switches 12, 15 and 15' to prevent arcing while the position of any switch lever is being changed. Assuming the preferable arrangement'in which all of the six winding sections shown in Fig. 5 have the same number of turns, then it will be seen that the maximum number of effective turns of the complete winding is four times the minimum number and that the secondary voltage adjustment has a correspondingly wide range. It will also be apparent that the voltage stress on the insulation of any part of the entire winding is at no time greater than the voltage applied at the terminals of the winding. The range of voltage adjustment may be indefinitely increased'by the addition in this manner of pairs of intermediate winding sections each provided with tap connections and a tap changing switch.

It will be apparent upon consideration of the drawings that this invention provides an arrangement whereby the effective number of turns of a transformer winding may be increased and decreased throughout a wide range without interrupting its operation and without at any time subjecting any portion of the winding orits insulation to a voltage stress greater than the voltage of the circuit which supplies current to the winding. The winding need be insulated therefore only for this supply circuit voltage.

The principles of the invention have been explained by describing it as applied in the construction and method of operation of the primary winding of a step-down transformer but it is obvious that the invention may be applied to either winding of either a step-down or step-up transformer.

What I claim as new and desire to secure by Letters Patent of the United States, is,-

1. A transformer comprising a winding having four sections, each section being provided with a plurality of taps, means for connecting one end of each section to any selected tap of one of the other sections, and means for connecting the other ends of two of said sections across an external circuit.

2. A transformer comprising a winding having two line sections and two intermediate sections, each of said sections being provided with taps, means for connecting one end of one of said line sections to any selected tap of one of said intermediate sections, means for connecting one end of the other of said line sections to any selected tap of the other of said intermediate sections, means for connecting the other ends of said line sections across an external circuit. means for connecting one end of one of said intermediate sections to any selected tap of one of said line sections. and means for connecting one end of the other intermediate section to any selected tap of the other of said line sections.

3. A transformer comprising a winding having two line sections and two intermediate sections, each of said sections being provided with taps, means including a reactance for connecting one end of one of said line sections to any selected tap of one of said intermediate sections, means including a reactance for connecting one end of the other of said line sections to any selected tap of the other of said intermediate sections, means for connecting the other ends of said line sections across an external circuit, means for connecting one end of one of said intermediate sections to any selected tap of one of said line sections, and means for connecting one end of the other intermediate section to any selected tap of the other of said line sections.

4. A transformer comprising a winding having two line sections and a plurality of pairs of intermediate sections, each of said sections being provided with a plurality of taps, means for connecting a selected number of turns of one section of each pair of intermediate sections between one end of one of said line sections and any selected tap of the second line section, means for connecting a selected number of turns of the other section of each pair of intermediate sections between one end of said second line section and any selected tap of the first line section, and means for connecting the other ends of said line sections across an external circuit.

5. A transformer comprising a winding having two line sections and a plurality of pairs of intermediate sections, each of said sections being provided with a plurality of taps, means r connecting a se ected numher of turns of one section of each pair of intermediate sections between one end of one of said line sections and any selected tap of the second line section, means for conmeeting a selected number of turns of the section, each of said connecting means including a circuit breaker, and means for conncctingthe'other ends of said line sections across an external circuit.

In witness whereof, I have hereunto set my hand this 14th day of June, 1923.

LOUIS F. BLUME. 

